Corrugated plastic conduit has started to replace electrical metallic conduit as a raceway for insulated conductors. In order to attach the electrical conduit to an enclosure or to connect the two ends of the conduit together, connectors are used which can either be glued or attached mechanically to a plastic corrugated conduit. Connectors of the type disclosed in applicant's U.S. Pat. No. 4,575,133, issued on Mar. 11, 1986, have found good market acceptance because of the ease of installation. Such a connector comprises a cavity receiving the extremity of the conduit, in which protrude one or more resilient tongues. Each tongue has an oblique camming surface facing the conduit entry end of the cavity and an opposite vertical locking face. In order to attach the connector to the conduit, the electrician has only to cut the conduit to the required length and insert it into the cavity of the connector. During the insertion operation, the ribs on the conduit cam the tongues out of the way allowing the conduit to slide easily past the tongues. Once fully inserted, the conduit is prevented from being pulled out of the connector by virtue of the interference created between the locking faces of the resilient tongues and a conduit corrugation.
The connectors for a corrugated conduit are normally manufactured by the well known injection moulding process. A typical set-up used for this purpose comprises a solid core positioned into the shaping mould to form the conduit receiving cavity of the connector. On the core is machined a recess to form the resilient tongue of the connector. At the end of the moulding cycle, after the part is cooled and the plastic material has solidified, the mould opens apart along the parting line and the connector is stripped of the core using an ejector assembly. A difficulty arises because of the interference created between the locking face of the tongue and the recess on the core. Should one try to eject the connector, the projection will likely be sheared off.
One method to solve this problem is to use a collapsible core of the type described in the U.S. Pat. Nos. 3,247,548 and 3,660,001. This core, although commercially produced, is expensive and difficult to maintain as the plastic material in fluid state may enter the core joints and cause a malfunction. In addition, the moulding operation is slowed down because of poor heat transfer between the cooling medium, the core and the moulded part.
Another approach is to use a two part connector of the type commercialized under the trademark KWIKON. One part of the connector contains the holding tongues and the other part is an outer ring pressed on the connector body. The tongues are very flexible in order to allow the removal from the core and by themselves they have no power to prevent the forceful removal of the conduit from the connector. The ring, when pressed on the connector, holds the tongues more rigidly in place. This type of connector operates well, however, the production methods are fairly costly as the two parts have to be moulded separately and then assembled.